A woman from Mexico is suing the U.S. government after Border Patrol agents shot and killed her husband during a family picnic on the south side of the international boundary.

Guillermo Arévalo Pedraza, 37, was fatally wounded on September 3, 2012, according to his widow, Nora Isabel Lam Gallegos, who has filed a lawsuit against six Border Patrol agents, former Homeland Secretary Janet Napolitano, and other government officials.

Lam claims Border Patrol agents opened fire from an airboat on the Rio Grande, which serves as a border between the two countries. The gunfire struck Arévalo, who was picnicking with his wife and two daughters for a birthday celebration at a Mexican park along the river.

“As the family laughed, played, and cooked with others alongside the river, the agents, without warning or provocation, opened fire on the crowd. Two bullets struck Arévalo—one in the abdomen and one in the leg,” the lawsuit states.

“The agents in the airboat quickly fled the scene of their crime, rendering no assistance to the dying Arévalo,” it further says.

Customs and Border Protection said in a prepared statement that the agents used deadly force in response to rocks being thrown at them from the Mexican side of the river.

Witnesses have disputed the agency’s assertion about the rock throwing. A video reportedly shows the agents were “far beyond the distance” that any rock could have hit them, according to Courthouse News Service. Border Patrol agents often use the excuse that rocks are being thrown as a handy excuse for firing on people on the south side of the border.

Witnesses say the agents were harassing a swimmer who had apparently tried to cross to the United States and then went back toward the Mexican side of the river. When Mexican families shouted at the agents to leave the swimmer alone, the agents fired into Mexico, according to the complaint.